The current invention is generally related to image projectors or image projection methods, and more particularly related to a correction of the projected image when the optical axis of a projector is positioned at a non-perpendicular angle with respect to an image-projection surface.
It is an important issue for screen projectors to project a digitally formed image on a projection surface without any distortion. In prior art, a frequent problem for using a screen projector is a keystone distortion associated with an imperfectly orthogonal angle between the projection screen surface and an optical axis of the projector. In other words, the project is often positioned at an angle that is not perpendicular to the screen. In order to correct the keystone distortion, the following prior art approaches have been proposed. A typical prior art correction technique repositions the optical system or the projector itself. In this technique, a lens is re-positioned to be in parallel with the image-forming plane, and this technique has been embodied in a number of practical examples. Unfortunately, this technique requires a costly precision lens since an image is formed on a wide-angle side. A second technique is to correct the distortion by adding a wedge-shaped lens and prism in the optical system. The second technique also requires additional optical parts, and consequently, the system is costly for correcting a large amount of distortion.
Another prior attempt digitally corrects the keystone distortion in projected images. A typical correction involves the projection of a known test pattern in a fixed projection environment, and a digital camera takes an image of the projected pattern. Based upon the captured image, an amount of the distortion is calculated. An image-forming source is positioned to compensate the distortion amount. Unfortunately, this prior solution requires a separate image-capturing device such as a digital camera.
In view of the above-described prior art, it remains desirable to provide a projector that is equipped with an adjustable correction mechanism for a user to easily correct distortions, which are caused by the conditions under use and are different from expected distortions at the design stage.
In order to solve the above and other problems, according to a first aspect of the current invention, a method of projecting an image, including: projecting an image-forming surface onto an image-projection surface by a projector, the image-forming surface containing an image, an optical axis of the projector being positioned at a non-perpendicular angle with respect to the image-projection surface; inputting focus data to adjust focus; and mechanically adjusting an angle of an image-forming component of the projector with respect to the image projection surface based the focus data, the image-forming component including a lens and an image-forming plate, wherein the image is focused on the image-projection surface.
According to a second aspect of the current invention, a system for projecting an image, including: an optical unit for projecting an image-forming surface onto an image-projection surface by a projector, the optical unit including an image-forming component, the image-forming surface containing an image, an optical axis of the image-forming component initially being positioned at a non-perpendicular angle with respect to the image- projection surface; an input unit connected to the optical unit for inputting focus data to adjust focus; and an angle adjustment unit connected to the image-forming component for mechanically adjusting an angle of the image-forming component with respect to the image projection surface based the focus data, wherein the image is focused on the image-projection surface.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.